Towards a safer material for artificial muscles

Whether it’s wiggling our toes or picking up grocery bags, the muscles in our bodies gently expand and contract. Some polymers can do the same thing—act like artificial muscles—but only when stimulated with dangerously high voltages.

Now Yeerlan Adeli, Francis Owusu, Frank A. Nüesch and Dorina M. Opris, all from the Swiss Federal Laboratories for Materials Science and Technology (EMPA), have succeeded in creating a series of thin, elastic films that respond to electrical charges very much. lower. These materials represent a key step toward making artificial muscles that may one day function safely in medical devices.

Artificial muscles could become key components of mobile soft robotic implants and functional artificial organs. Electroactive elastomers, such as bottlebrush polymers, are interesting materials for this purpose because they are initially soft but harden when stretched. Also, they can change shape when electrically charged. However, currently available bottlebrush polymer films only move at voltages above 4,000 volts, which exceeds the 50 volt maximum that is considered safe by various agencies, such as the US Occupational Safety and Health Administration. Reducing the thickness of these films to less than 100 microns could lower the stresses required, but successfully doing this for bottlebrush polymers has been beyond the reach of the scientific community. So Dorina Opris and her colleagues wanted to find an easy way to produce finer film.

The researchers synthesized a set of bottlebrush polymers by reacting grafted polydimethylsiloxane macromonomers with norbornene and crosslinking the products using ultraviolet light. A 60 micron thick material was the most electroactive, with higher expansion than previous elastomers and an operating voltage of 1000 volts. And a circular actuator made of that material expanded and contracted more than 10,000 times before breaking down. In another series of experiments, the researchers introduced polar side chains into polymers and produced materials that responded to voltages as low as 800 volts. However, they did not expand as much as the more electroactive film on the team. Based on the results, the researchers say that, with a few tweaks, the material could one day be used to develop durable implants and other medical devices that operate at safer voltages.

Artist’s impression of an android’s arm with artificial muscles pitted against a human’s arm, with natural muscles. (Illustration: NASA JPL / Carolina Martinez)

The study is titled “On-Demand Cross-Linkable Bottlebrush Polymers for Voltage-Driven Artificial Muscles”. And it has been published in the academic journal ACS Applied Materials & Interfaces. (Source: American Chemical Society)